In order to respect the increasingly lower emission restrictions imposed by recent anti-pollution standards, electronic injection feeding instead of traditional carburetor feeding must also be used for low-powered internal combustion engines for motorcycles (also of only 50 cc).
In an electronic injection fuel feeding system for a low-powered internal combustion engine, an electrically operated fuel pump draws the fuel from a tank at atmospheric pressure and feeds the fuel itself to the injector; the fuel pump must have a very low electric power absorption, compatible with the electric power generated by the electric generator when the internal combustion engine is idling.
The amount of fuel which is injected by an injector depends on both the injection time (i.e. on the time interval for which the injector is kept open) and the fuel feeding pressure. Accordingly, when electronic injection feeding is used, the fuel feeding pressure must be guaranteed constant and equal to a predetermined design value.
In the known low-powered internal combustion engines, a constant flow rate and high-efficiency fuel pump (to keep the electric power consumption low) is used associated to a pressure regulator, which keeps the fuel feeding pressure constant and equal to the predetermined design value. Accordingly, the fuel pump always feeds a constant fuel flow rate to the injector regardless of the engine rate and the pressure regulator recirculates the fuel in excess back to the tank to keep the fuel feeding pressure constant and equal to the predetermined design value.
In other words, the fuel pump is dimensioned to feed an amount of fuel exceeding the actual consumption in all conditions of operation, and downstream of the fuel pump the pressure regulator is provided, which keeps the fuel feeding pressure value constant and equal to the predetermined design value by discharging the fuel in excess into a recirculation channel which re-introduces the fuel in excess itself back into the tank. In this case, the fuel pump must be dimensioned to feed an amount of fuel equal to the maximum possible consumption; however, such a condition of maximum possible consumption occurs rather rarely and in all the remaining conditions of operation the amount of fuel fed by the fuel pump is much greater than the real consumption and therefore a considerable amount of such fuel is to be discharged by the pressure regulator into the tank.
It is apparent that the work performed by the fuel pump for pumping the fuel which is later discharged by the pressure regulator is an “unnecessary” work, and therefore the electronic injection feeding system globally displays a very low energy efficiency. Furthermore, the pressure regulator and the recirculation channel connected to the pressure regulator are rather cumbersome and increase the total costs of the electronic injection feeding system.
In order to solve the above-described drawbacks, it has been proposed to use a fuel pump provided with a variable volume pumping chamber; a one-way intake valve; a one-way delivery valve; a mobile piston which integrates the intake valve therein and which is coupled to the pumping chamber to cyclically vary the volume of the pumping chamber itself; and an actuator device which imparts a reciprocating motion on the piston and displays an electromagnetic actuator to actuate the piston during a step of delivering.
JP58117351A discloses a fuel pump driving circuit which is suitable for electric power saving, by turning ON and OFF the fuel pump, and controlling the ON time in correspondence with the required amount.
WO2007031463A1 discloses a method for operating a fuel pump in order to guide fuel from the fuel container of an internal combustion engine, wherein the electric energy, which is in the form of pulses, is periodically guided to the fuel pump and the duration of the pulses is controlled according to the fuel required by the internal combustion engine. The frequency of the pulses is controlled in such a manner that, in the event of low pump capacity of the fuel pump, the frequency is controlled to a higher level than in the even of a high pump capacity.